Viral respiratory infections may alter pulmonary vascular responses to hypoxia and promote pulmonary edema formation, which is a central feature of many serious respiratory illnesses. The molecular mechanisms by which infections or hypoxia alter lung water remain incompletely explored. Previous work suggests that the vasoconstrictor peptide, endothelin (ET), contributes to pulmonary edema formation in these circumstances, perhaps by stimulating expression of vascular endothelial cell growth factor (VEGF). The precise mechanisms by which ET promotes edema formation in the lung remain uncertain, however, as does the contribution of VEGF to pulmonary edema formation. These uncertainties suggest that mediators other than VEGF may be important in ET-induced pulmonary edema formation. Ephrins are a family of receptor tyrosine kinase ligands and receptors with demonstrated roles in vascular development. Ephrins also mediate some pro-angiogenic effects of VEGF in systemic vascular beds. Preliminary data supports the hypotheses that ET stimulates lung VEGF and ephrin expression, and that VEGF and ephrin expression contribute to pulmonary edema formation. The specific aims of this proposal, then, are (1) to test the hypothesis that viral infection and hypoxia act via ET to increase lung VEGF expression and consequently to increase vascular permeability, and to study the molecular mechanisms of that effect in vitro; (2) to test the hypotheses that ephrin signaling leads to increased pulmonary vascular permeability both in vitro and in vivo and that ephrin signaling contributes to VEGF-induced permeability in the lung; (3) to test the hypothesis that viral infection and hypoxia act via ET to increase lung ephrin expression and that ephrins contribute to ET- and VEGF- induced increases in vascular permeability, and to study the molecular mechanisms of that effect in vitro. These studies will explore novel mechanisms contributing to pulmonary edema formation and may ultimately identify potential sites of therapeutic intervention in that process. [unreadable] [unreadable]